The Difference Between Helical Piles And Micropiles
In downtown Portland, a client planned to add a third story and seismic upgrades to a two-story building, built in the 1920s. A structural evaluation found that the building was constructed of unreinforced concrete and wooden frames. The proposed renovation required the installation of three columns supported by a grade beam of Reinforced Concrete, three feet in width and forty feet in length, underneath the building. This required inserting micropiles into the soil beneath the site. However, a geotechnical survey of the site revealed that the soil was composed of four feet of silt underlain by alluvial soil. This made the micropiles unsuitable as Structural Underpinning.
The client approached TerraFirma Foundation Systems, OR, and discussed the possibility of using Helical Piles instead of micropiles. A tension load test proved the Helical Piles suitable for the design load. In due course, the Helical Piles were installed to a depth of thirty-two feet below the bottom of the grade beam, with the construction brackets of the pile tops cast into it. The job was carried out in two days, with minimum disruption to the construction schedule. This Foundation Support procedure is a good example of Seismic Retrofitting that is available to property owners in Oregon.
To view the complete details of this case study, you may download the report here (pdf): Case Study: Helical Piles